Boston Fern
Nephrolepis exaltata · Sword Fern
It grows in humid American forests and swamps, both in the ground and clinging to tree trunks, throwing out long lacy fronds. The plant we keep is a sterile clone that turned up by accident in 1894.
Family
Nephrolepidaceae
Origin
Tropical Americas
In the wild
Grows on tree trunks
Indoors
0.4–0.9 m
Growth
Moderate
With pets
Safe
Where it's from
Tropical and subtropical Americas
Humid forest floor
Native to Florida, the West Indies, Mexico and Central and South America, in moist humusy shade.
Outdoors: zones 10–12
Frost-tender. A summer porch fern at most, brought inside before the cold across the US South.
An accidental escapee
So vigorous it is classed as an invasive alien plant in South Africa. Thriving at home and in the wild.
Born from a mistake
In 1894 a single oddball with unusually wide arching fronds turned up in a shipment of ordinary sword ferns sent to a Boston-area florist. It was a spontaneous sport, named 'Bostoniensis' for the city. Because it is sterile, every Boston fern alive is a clone, propagated by division, not seed or spore.
It cannot self-seed
The cultivar does not make spores that come true, so it is multiplied vegetatively.
It spreads by runners
Above-ground stems called stolons root into new plantlets, the easy way to propagate it.
The Victorian parlour fern
One of the signature potted ferns of the late 1800s, popular for over 130 years.
How to keep it
LightBright, indirect
Tolerates some shade, but no direct sun, which scorches the fronds.
WaterKeep evenly moist
Consistently moist, never fully dry. Dry soil browns the fronds quickly.
HumidityHighIts make-or-break field. Loves bathrooms and kitchens; low winter air browns the tips.
Temperature16–24°CWarm rooms, no frost.
SoilPeaty, soil-based mixMoist but well-draining.
FeedingLight, in growing seasonFerns are sensitive to over-feeding, so feed lightly.
DifficultyModerateAn easy plant whose humidity demand defeats many beginners.
With petsNon-toxicListed safe for cats, dogs and horses by the ASPCA. Large amounts of any plant can still cause mild upset.
PropagationDivision of runnersSeparate the plant or pin down its above-ground runners to root new plantlets.
RepottingEvery 1–2 yearsOr when root-bound. Divide at the same time.
What the data says
What it costs
A seasonal commodity, sold from every big-box garden centre and often discounted in spring.
$10–30
Specialty and dwarf cultivars run a little higher, but nothing approaches collector pricing.
The clean-air myth
A star of NASA's 1989 study, it cleared formaldehyde and other VOCs efficiently in a sealed test chamber.
100–1,000
plants per square metre would be needed to match a room's normal ventilation (Cummings and Waring, 2019). The 1989 chambers had no fresh air. Buy it because it is gorgeous and pet-safe.
IUCN · Least Concern
In the wild
Widespread and abundant, sometimes too much so.
So vigorous it is classed as an invasive alien plant in South Africa, and its close relative N. cordifolia is an aggressive invader in Florida and Hawaii. A reason to confirm which species you actually have.
When it sulks
Brown, crispy frond tipsThe number one complaint: low humidity, or the soil drying out.
Fronds dropping indoorsDry air, dry soil, or a sudden change of environment.
Yellowing frondsOverwatering and poor drainage, or too much sun.
PestsScale, mealybugs and whitefly. Treat early.
Shedding messMature plants drop dried pinnae. Normal, just messy.
Varieties & company
The varieties
BostoniensisFluffy RufflesWhitmaniiRooseveltiiDallas
Pairs with · keep apart from
CalatheaPrayer PlantPeace LilySnake PlantZZ PlantCacti
A new plant, every week.
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